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Re: [Bug 18] no record of consensus for force-authenticate

From: Julian Reschke <julian.reschke@gmx.de>
Date: Fri, 28 Oct 2005 15:47:27 +0200
Message-ID: <43622BEF.3060706@gmx.de>
To: Jim Whitehead <ejw@soe.ucsc.edu>
CC: WebDav <w3c-dist-auth@w3.org>

Jim,

thanks for doing the "right thing" here. Comments inline.

Jim Whitehead wrote:
>  ...
> SOLUTION REQUIREMENTS
> 
> R1: A client must be able to request an authentication challenge  
> without causing a state change on the server
> R2:  The mechanism for the authentication challenge must be clearly  
> identifiable within the specification
> R3: The client must be able to indicate which method the challenge  
> pertains to (since this can potentially vary by method, though it  
> usually doesn't)
> 
> SOLUTION PROPOSAL
> 
> I like the Force-Authenticate header as defined in the current draft.  I 
> don't like the If approach (submit an If header with a known bad  lock 
> token, hence the method will fail) for three reasons:
> 
> * I feel uncomfortable depending on an unintended use of the If  header 
> -- especially for PUT, if a server ever doesn't handle If  correctly, 
> the forcing of authentication could inadvertently change  the contents 
> of the resource (assuming you'd force authentication  with a zero length 
> body with PUT)

I don't feel that we should add new features to the spec just because we 
fear that some servers may not get the existing stuff right. I a server 
doesn't handle the If header correctly upon PUT, this is a bug that 
needs to be fixed anyway.

As a matter of fact, of the servers I recently tested 
(<http://lists.w3.org/Archives/Public/w3c-dist-auth/2005OctDec/0328.html>), 
two were failing here, one of which not doing "If" checks at all, the 
other one treating unknown state tokens incorrectly. The latter is 
moddav, the bug is reported in 
<http://issues.eu.apache.org/bugzilla/show_bug.cgi?id=37288>, and Joe 
Orton has already attached a proposed patch.

The other servers (SAP Netweaver, Xythos, MS IIS) work as expected.

> * It depends on the execution order of authentication vs. If header  
> processing within servers (I note this was rebutted in:
> http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JulSep/ 0335.html  
> and I also note that mod_dav does do authentication checks  before If 
> checks)

Yep. Is anybody aware of servers working differently.

> * It's a really obscure way of satisfying the requirements (i.e., it  
> fails requirement R2)

That can be fixed by putting that as note into an appendix.

> My strong preference is for a new mechanism here (Force- Authenticate), 
> though I could perhaps be swayed to adding a new  section to the 
> specification that explicitly describes the use of If  to force 
> authentication, and gives an example of how this works. I  don't think 
> this mechanism is one that most implementors would think  of, even if 
> the have a deep understanding of the spec (like, me, for  example, who 
> never thought of this).

I have no problem adding non-normative text explaining this.

On the other hand I'd really like to hear from those client 
implementors. After the three years ago, did anybody actually try the 
solution proposed back then? If not, why not?

Best regards, Julian
Received on Friday, 28 October 2005 13:48:25 GMT

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